[Buildroot] [PATCH] pkg-cmake: use -fPIC

[Samuel Martin]

Hi Francois,

On Sun, Feb 16, 2014 at 5:29 PM, François Perrad
<francois.perrad at gadz.org> wrote:
> 2014-02-16 11:51 GMT+01:00 Samuel Martin <s.martin49 at gmail.com>:
>> Hi Francois,
>>
>> On Sun, Feb 16, 2014 at 11:05 AM, Francois Perrad <fperrad at gmail.com> wrote:
>>> fix build for lua-ev
>>> http://autobuild.buildroot.org/results/730/7303fffa6075d02289b6fdb12a1debdf0dd7d6f1//build-end.log
[...]
>>
>> Usually, PIC properties is set at the cmake target level, but this
>> property is driven by the global variable
>> CMAKE_POSITION_INDEPENDENT_CODE (see:
>> http://www.cmake.org/cmake/help/v2.8.12/cmake.html#prop_tgt:POSITION_INDEPENDENT_CODE)
>>
>> I would prefer using this variable, it should not break anything if
>> some projects set this property otherwise.
>>
>
> You are right, my patch is too invasive.
>
> BUILD_SHARED_LIBS is correctly set in pkg-cmake.mk by :
>      -DBUILD_SHARED_LIBS=$(if $(BR2_PREFER_STATIC_LIB),OFF,ON)
>
> And the CMakeLists.txt of lua-ev contains :
>      ADD_LIBRARY(cmod_ev MODULE lua_ev.c)
>
> The CMake documentation (see
> http://www.cmake.org/cmake/help/v2.8.12/cmake.html#command:add_library)
>  said :
>       "For SHARED and MODULE libraries the POSITION_INDEPENDENT_CODE
> target property is set to TRUE automatically."
>
> So, I don't know what to do.

Looking carefully at the culprit build config you point above, it
appears BR2_PREFER_STATIC_LIB is not set, so in that case it makes
sense (to me) to set CMAKE_POSITION_INDEPENDENT_CODE.

Because when static libraries are built in such a configuration, they
can be used to built shared ones, so it's better if the *.a has been
built with -fPIC.

So, I tend to think that we could add to the configure options of the
cmake infra:
  -DCMAKE_POSITION_INDEPENDENT_CODE=$(if $(BR2_PREFER_STATIC_LIB),OFF,ON)

but this needs more investigations and tests.


Regards,

-- 
Samuel